Assume that two parties, A and B, want to sign a contract over a communication network, i.e. they want to exchange their “commitments“ to the contract. We consider a contract signing protocol to be fair if, at any stage in its execution, the following hold: the conditional probability that party A obtains B's signature to the contract given that B has obtained A's signature to the contract, is close to 1. (Symmetrically, when switching the roles of A and B). Contract signing protocols cannot be fair without relying on a trusted third party. We present a fair, cryptographic protocol for signing contracts that makes use of the weakest possible form of a trusted third party (judge). If both A and B are honest, the judge will never be called upon. Otherwise, the judge rules by performing a simple computation, without referring to previous verdicts. Thus, no bookkeeping is required from the judge. Our protocol is fair even if A and B have very different computing powers. Its fairness is proved under the very general cryptographic assumption that functions that are one-way in a weak sense exist. Our protocol is also optimal with respect to the number of messages exchanged.
|Original language||American English|
|Title of host publication||Automata, Languages and Programming - 12th Colloquium|
|Number of pages||10|
|State||Published - 1985|
|Event||12th International Colloquium on Automata, Languages and Programming, ALP 1985 - Nafplion, Greece|
Duration: 15 Jul 1985 → 19 Jul 1985
|Name||Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)|
|Conference||12th International Colloquium on Automata, Languages and Programming, ALP 1985|
|Period||15/07/85 → 19/07/85|
Bibliographical noteFunding Information:
1 Institute of Mathematics and Computer Science, Hebrew University, Jerusalem, Israel. Work done when visiting MIT's Lab. for Comp. Sc. Supported by a Weizmann Postdoctoral Fellowship. 2 Computer Science Dept., Technion, Haifa, Israel Currently in the Lab. for Comp, So, MIT. Supported by a Weizmann Postdoctoral Fellowship. 3 LaboratoD, for Computer .Science, MIT, Cambridge, MA 02139, USA. Supported by NSF Grant DCR-8413577 and an IBM Faculty Development Award. 4 I~boratory for Computer Science, MIT, Cambridge, MA 02139, USA, Supported by NSF Grant MCS80-06938.
© 1985, Springer-Verlag.